Issues concerning passenger safety have become increasingly important as the speed of the vehicles transporting these passengers has increased. In an attempt to reduce injuries due to the sudden accelerations produced in vehicle collisions, a number of passenger restraint systems have been employed. These restraint systems have commonly employed belts and/or harnesses which fasten about the passengers in order to achieve two primary objectives: (1) Maintaining the passenger's original orientation and position within the vehicle; (2) Absorbing the passengers' kinetic energy.
These restraint systems are most effective when the harness is highly tensioned about the passenger prior to the onset of the acceleration force which propels the passenger's body against the restraining harness. However, if applied to the harness at all times, this level of tension restricts the movement of the passenger and reduces passenger comfort.
Thus there is a need for a restraint system including a harness or belt which is immediately tensioned about a passenger in response to an acceleration of the vehicle which is potentially injurious to the passenger.
Known restraint systems have attempted to utilize power from an external source to tension restraint harnesses. However, these systems have employed sensors and a preset action threshold to activate the harness tensioning. Consequently, these systems are complex and expensive and display little flexibility as to the amount of belt tensioning effected in response to various accelerations.
Systems are known which utilize the inertial force of a movably mounted counterweight to tension the belt about the passenger. However, although the acceleration acting on the counterweight is identical to that acting on the passenger, such systems provide a tensioning force which is not proportional to the inertial force of the passenger. That is, because the mass of the counterweight is constant, these systems do not provide a tensioning force which varied in proportion to the inertial force of the passenger.
In addition, devices are known which utilize the motion of a passenger seat in response to a vehicular acceleration to drive a mechanism which tensions the seat belt. In these devices, the action of the seat motion on the belt anchors works in opposition to the passenger's inertial forces translated by the belt. The timing of these devices is inherently late, being responsive only after the accelerating force has become appreciable enough to cause significant seat motion, and hence has already caused the passenger to be heavily forced upon the harness. In fact, this timing delay can even magnify potential dangers. The risk of whiplash induced by recoil is increased. In addition, the force of the passenger on the belt prior to the tightening action may exhaust the belts elastic capacity to absorb energy from the passenger before the tightening action increases the belt tension to potentially hazardous levels.
Thus there is a need for a relatively simple restraint system which provides a timely tensioning force which is proportional to the inertial force of the passenger and which works in synchronization with, or without a moving seat.